CO2 Provision for Urea Synthesis via Pressure-Shifted Absorption
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Solution Overview
Problem
Current methods for large-scale urea production, which integrate ammonia and urea plants, face inefficiencies in energy usage and equipment costs due to the need for significant energy and equipment to compress carbon dioxide to the required pressure level, and introduce excessive water, affecting the urea formation equilibrium and energy balance.
Innovation Solution
A method involving a gas stream separation using a solvent to remove carbon dioxide, followed by ammonia synthesis and desorption of carbon dioxide at a higher pressure than urea synthesis, allowing for efficient use of reaction heat and minimizing additional water input, thereby reducing energy requirements and equipment needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If carbon dioxide is separated from synthesis gas using regenerative gas scrubbers with selective solvents, then carbon dioxide can be obtained for urea synthesis, but disproportionately greater energy and equipment effort is required to compress gaseous carbon dioxide to the pressure level of the urea plant
Solution Approach 1:
The patent changes the physical state of carbon dioxide from gaseous to liquid form by conducting the absorption process under elevated pressure conditions. This parameter change allows the carbon dioxide to be transported in liquid form through the process system, eliminating the need for high-energy compression equipment while maintaining the required pressure level for urea synthesis
Solution Approach 2:
The ammonia-water mixture serves multiple functions: it acts as the absorbing solvent for carbon dioxide separation, provides the liquid phase medium for carbon dioxide transport, and maintains the pressure level required for urea synthesis. This multi-functionality eliminates the need for separate compression equipment
2Use of energy by moving object
If complete carbon dioxide removal from synthesis gas is performed using process-integrated ammonia absorption, then energy requirement for CO2 compression is reduced, but a considerable additional amount of water is introduced into the urea synthesis, which has an unfavorable effect on the equilibrium of the urea formation reaction
Solution Approach 1:
The patent applies partial absorption by removing only the necessary amount of carbon dioxide from the synthesis gas to meet urea synthesis requirements, rather than complete removal. This partial action prevents excessive water from being introduced into the urea synthesis process while still achieving the required carbon dioxide supply
Solution Approach 2:
The process incorporates feedback control where the carbon dioxide-rich ammonia-water solution is circulated and the carbon dioxide content is regulated to match the exact requirements of the urea synthesis unit, preventing over-introduction of water into the reaction system
3Ease of operation
If carbon dioxide is absorbed by ammonia or ammonia-water mixtures to form carbamate, then carbon dioxide can be transported with comparatively little effort, but a lot of heat is released when carbamate is formed, requiring cooling that dissipates energy and requires additional energy for the urea reactor
Solution Approach 1:
The patent converts the harmful effect of heat release during carbamate formation into a beneficial resource. The exothermic heat of absorption is captured and utilized to provide the endothermic heat required for the urea decomposition reaction, transforming an energy loss into an energy source that improves overall process efficiency
Solution Approach 2:
The patent merges the absorption process with the urea synthesis process by directly feeding the carbon dioxide-rich ammonia-water solution from the absorber into the urea synthesis unit. This integration allows direct heat transfer from the exothermic absorption zone to the endothermic synthesis zone, eliminating separate cooling and heating requirements
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces energy consumption by utilizing the heat of reaction and eliminating the need for a carbon dioxide compressor, while maintaining the urea yield and avoiding excessive water input, making it suitable for large-scale production.
Implementation Method 1
separating at least part of the carbon dioxide from gas stream A with a solvent to form a carbon dioxide-depleted gas stream B and a carbon dioxide-laden solvent
Implementation Method 2
The carbon dioxide is mainly chemically bound in the solution in the form of carbamate and carbonate ions
Implementation Method 3
desorption of the carbon dioxide from the loaded solvent from step (b)
Implementation Method 4
The urea synthesis from ammonia and carbon dioxide is exothermic overall. It consists of the relatively strongly exothermic and relatively fast reaction of the educts to form ammonium carbamate
Implementation Method 5
the significantly slower and endothermic decomposition of the carbamate to form urea and water
Data Source
Figure 1
AI summary
The invention relates to a method for the separation of carbon dioxide from CO2-containing gases and to a device for the provision of carbon dioxide for the synthesis of urea.